FIG. 11 shows an outline of a flash-butt welder. The flash-butt welder is provided with a stationary head 41 and a moving head 42. Each of the heads has hydraulic cylinders 43a, 44a, and 43b, 44b, to clamp a preceding billet 10a and a succeeding billet 10b, respectively. Of these hydraulic cylinders, the clamp bodies of the cylinder 43a and of the cylinder 43b which are near to an edge 11 of the billets form electrodes 45, 46, respectively. The moving head 42 is movable, and the movement thereof is controlled by a plurality of upset hydraulic cylinders (not shown).
FIG. 12 illustrates the arrangement of the power source transformers and the conductors (bus bars) in the flash-butt welder shown in FIG. 11. The stationary head 41 is equipped with two power source transformers 12, 13, and the moving head 42 is also equipped with two power source transformers 14, 15. Each of the four bus bars, 16 through 19, connects a transformer of the stationary head 41 side with the corresponding transformer of the moving head 42 side.
A flash-butt welder for welding billets or the like uses a power source with low voltage and large current (for example, 10 Volts and 100 thousand Amperes) owing to the inherent characteristics of the welder. Consequently, the welder requires at least four transformers, 12 through 15, and furthermore, each two power source transformers are provided to each of the stationary head 41 side and the moving head 42 side, as shown in FIG. 12. As a result, the necessary number of bus bars connecting the stationary head 41 side with the moving head 42 side is at least four. This requirement makes the structure of the welder complex, and these bus bars cause a high impedance. The high impedance results in a low efficiency. Since the welder is driven under a condition of low voltage and large current, the effect of the high impedance is extremely significant.